The tilting disc heart valve prosthesis is becoming increasingly popular as a replacement for aortic and mitral valves. However, clinical results have been reported that suggest poor hydraulic performance at particular valve orientations. Bjork, designer of the Bjork-Shiley tilting disc prosthesis, has reported a 26% incidence of embolization when the disc of the mitral prosthesis opens towards the ventricular septum. It is the purpose of this work to document hydraulic performance of the tilting disc at all possible orientations so as to help the surgeon place the prosthesis in its optimum position at implantation. The valve testing techniques have been developed and extensively used in this center over the last 10 years, and only the valve test chamber of our pulsatile flow testing apparatus needs to be modified in order to carry out the proposed experiments. This work would be part of a comprehensive program of the Reconstructive Cardiovascular Research Center, where biologic testing of promising developments will be carried out.